Build and check EPUB documentation

Author: m-aciek

.github/workflows/reusable-docs.yml

@@ -75,6 +75,13 @@ jobs:
           --fail-if-regression \
           --fail-if-improved \
           --fail-if-new-news-nit
+    - name: 'Build and check EPUB documentation'
+      continue-on-error: true
+      run: |
+        set -Eeuo pipefail
+        make -C Doc/ PYTHON=../python SPHINXOPTS="--quiet --fail-on-warning" epub
+        pip install epubcheck
+        epubcheck build/epub
 
   # Run "doctest" on HEAD as new syntax doesn't exist in the latest stable release
   doctest: